Inductive cores and core components are utilized in a vast number of electronic applications. One example implementation is switched mode power supply (SMPS), a common form of power supply that is utilized in a wide variety of electronic devices, as can be appreciated by one skilled in the art. Other applications include transformers, power converters, power generators, power conditioning components, and inductors, which for example can be used in Electronically Scanned Phased Arrays (ESPA) and Electronic Warfare (EW) systems, conditioning components for wireless and satellite communication, radar systems, power electronics, inductive devices, and systems, devices, or electronics utilizing switched-mode power supplies.
The example of SMPS can be useful in explaining some of the requirements and demands placed upon core components. Generally, SMPS involves the repeated switching of an input power supply between full-on and full-off. The rate of switching is measured as a frequency. Input power flowing through such a system can be changed in many ways in order to produce a particular desired output signal, as can be appreciated by one skilled in the art. For example, input power can be rectified, converted, cycloconverted, transformed, inverted, as well as many other changes in amplitude or phase associated with AC-to-AC power supplies, AC-to-DC power supplies, DC-to-DC power supplies, and DC-to-DC power supplies. All such changes can be controlled in specific manners to produce an output power level having particular desired voltage and/or current characteristics.
SMSP achieves greater efficiency over other competing power supplies, such as linear power supply, by capturing and storing energy in a “core.” A core is a structural component (utilized in SMPS systems and also a wide range of other systems) that is made from magnetic material(s) and that can store energy generated by the system. Magnetic materials are used to make cores because they possess a high capacity for storing magnetic fields, a convenient and useable form of energy in such applications. Cores often are built from materials such as soft ferrites, since these materials exhibit high magnetization, low conductivity, and low coercivity (low remnant magnetization).
Continuing with the example of SMPS, higher switching frequencies in SMPS are associated with a number of known benefits, such as higher power efficiency. Increased switching frequencies also enable size reduction in SMPS systems, since smaller switching periods result in lower storage requirements. Said differently, a higher switching frequency results in a smaller amount of time during which a magnetic field is induced (i.e., stored) in the core, which causes the magnetic field in the core to be smaller, enabling the core itself to be reduced in size.
However, the maximum switching frequency is constrained by particular types of power losses in the core that become more noticeable at higher frequencies. In particular, as the operating frequency rises, power efficiency becomes highly dependent on “Eddy current losses” (i.e., losses due to the formation of Eddy currents within the core). Minimizing the presence and effects of Eddy currents typically becomes the most important factor in improving core characteristics, particularly for high frequency power ferrites. One known way to reduce core losses due to the appearance of Eddy currents in the ferrite material is to increase the resistivity of the core material, since resistivity restricts current flow in general, and restricts the flow of Eddy currents in particular. One skilled in the art can appreciate that by limiting the motion of electrons, Eddy currents become increasingly difficult to induce, thereby limiting the associated losses.
Accordingly, some attempts to limit Eddy current losses involve interspersing one or more highly resistive insulating materials at the grain boundaries of the grain material of the core, in order to prevent electron flow through the insulators and thus through the core. However, such attempts often fall short of providing cores that are capable of operating at extremely high frequencies (e.g., >1 MHz). Other efforts to reduce Eddy current losses involve implementing ferrite materials with high resistivity. These efforts suffer from a similar shortcoming of higher power losses at extremely high frequencies, as well as reduced overall permeability of the core material.
In many instances, the unsatisfactory performance at high frequencies is due to the fact that specification demands tend to place contradicting physical requirements upon cores. It is often difficult or impossible to optimize several magnetic properties simultaneously, due to the interdependency of the magnetic properties. Thus, improving one property may lead to the degradation of several others. As a result, existing core materials fail to satisfy the increasingly stringent high frequency requirements.
One skilled in the art can appreciate that the problems associated with cores described herein with respect to SMPS similarly exist for cores when applied to other systems and applications that do not utilize SMPS. In general, existing inductive cores are unable to meet the desired specification requirements, particularly at high frequencies.